WildFact
›
Information Section
›
Extinct Animals
›
Pleistocene Big Cats
Giant cheetah-Acinonyx Pardinensis
Giant cheetah-Acinonyx Pardinensis
|
Giant cheetah-Acinonyx Pardinensis
|
Synchrotron radiation reveals the identity of the large felid from Monte Argentario (Early Pleistocene, Italy)
Abstract We describe here a partial skull with associated mandible of a large felid from Monte Argentario, Italy (Early Pleistocene; ~1.5 million years). Propagation x-ray phase-contrast synchrotron microtomography of the specimen, still partially embedded in the rock matrix, allows ascribing it reliably to Acinonyx pardinensis, one of the most intriguing extinct carnivorans of the Old World Plio-Pleistocene. The analysis of images and 3D models obtained through synchrotron microtomography – here applied for the first time on a Plio-Pleistocene carnivoran – reveals a mosaic of cheetah-like and Panthera-like features, with the latter justifying previous attributions of the fossil to the extinct Eurasian jaguar Panthera gombaszoegensis. Similarly, we reassign to A. pardinensis some other Italian materials previously referred to P. gombaszoegensis (sites of Pietrafitta and Ellera di Corciano). The recognition of Panthera-like characters in A. pardinensis leads to reconsidering the ecological role of this species, whose hunting strategy was likely to be different from those of the living cheetah. Furthermore, we hypothesise that the high intraspecific variation in body size in A. pardinensis can be the result of sexual dimorphism, as observed today in all large-sized felids. Head appearance of Acinonyx pardinensis. The reconstruction is based on the complete skull from Pantalla6 and is updated with the information on the craniodental anatomy of A. pardinensis achieved from the Monte Argentario specimen. Artwork by D. A. Iurino.  *This image is copyright of its original author Acinonyx pardinensis from Monte Argentario. Specimen ArgBsc1 in right lateral (a), rostral (b), and left lateral (c) views. Scale bar: 50 mm.  *This image is copyright of its original author Results External observations The specimen (ArgBsc1) is represented by the rostral portion of the skull with associated mandible of a large felid (Fig. 2, Table 1). The neurocranium is almost completely missing, with only a small portion of the left frontal bone being visible. The splanchnocranium is better preserved on the left side, from which it looks rather shortened and dorsoventrally expanded. The zygomatic arches are lacking, as well as the orbits, with the exception of the dorsal margin of the left one, which is delimited by the postorbital process of the frontal. In rostral view, the nasal apertures look broad though slightly distorted, with the median part of the nasal bones being crushed into the nasal cavities. The mandible preserves the complete right corpus articulated with the anterior portion of the left one, broken at the level of the distal margin of the p4. Two mental foramina are visible on both sides, located at the same height immediately behind the distal margin of the lower canine and a few centimetres behind, respectively. Both the ascending rami are lost. The teeth are virtually unworn and in variable state of conservation. Only the roots of the right I3 and i3 are visible in rostral view. The left canines are missing, but the distoventral portion of the lower canine root is still preserved, delimiting a wide pulp cavity. Conversely, the canines on the right side are almost intact and stand out to be robust and elongated. A short distance separates the upper canine from the P3. The latter is broken on the right side, but complete on the left. It is characterised by a high, vertical, and pointed paracone. The right P4 is a large and robust tooth. In labial view, it shows, from front to back, a strong parastyle, a high and vertically-oriented paracone and a slightly shorter metacone. The root of the small M1 is visible distally to the right carnassial. With the exception of the canine, the other lower teeth are impossible to describe because they are covered by the upper teeth or the embedding matrix. The latter is a highly consolidated red-rust coloured claystone very hard to remove mechanically without the risk of damaging the fossil. This led to the need to examine the specimen through a highly performing x-ray image analysis technique. Discussion The identification of the specimen (ArgBsc1) based solely on external observation is hard, since the enclosing in the rock matrix makes very difficult the analysis of diagnostic characters, especially in the teeth. From the outside, the skull shows a series of intermediate Acinonyx-like and Panthera-like characters. The first include the high and short muzzle, the straight ventral margin and the right rostroventral angle of the mandible. The second include the relatively narrow frontals and especially the massive canines, mainly the upper ones, housed in prominent canine eminences. In particular, the latter characters might have led to the past erroneous attribution of the specimen to P. gombaszoegensis18, whose stratigraphic occurrence partially overlaps that of A. pardinensis. This may have been due also to the limited past knowledge of this taxon’s anatomy, which has increased significantly thanks to new discoveries in recent decades. In this regard, it is worth mentioning two other cases of misleading identification involving the same taxa. The first concerns Pietrafitta, a central Italian site with an age comparable to that of Monte Argentario25, the second the slightly older locality of Ellera di Corciano26. The scarce felid material from the two sites were referred in the past to P. gombaszoegensis27,28,29,30 and cf. P. gombaszoegensis31,32, respectively. The fossils are here reassigned to A. pardinensis (Supplementary Note 1 and Supplementary Figs S1–S2). The study of images obtained through the SR-µCT survey resulted in many additional information for the definition of the taxonomic status of the Monte Argentario skull. The following craniodental features identified on the 3D models of ArgBsc1 are consistently found in the other specimens attributed to A. pardinensis6,12,33 and differ from pantherine felids:
Similarly, most of the above characters allow to exclude that the Monte Argentario specimen can be referred to the late Pliocene-Early Pleistocene puma-like felid Puma pardoides34,35. In fact, although the latter species shows some similarities with A. pardinensis (e.g., lateral enlargement of the frontals caudally to the zygomatic processes and relatively shortened muzzle)6,33, differences between them are remarkable (e.g., Pu. pardoides has labiolingually enlarged P3, P4 with strong Panthera-like protocone, p3 significantly lower than p4 in labial view both showing more massive protoconid)5,6. Moreover, the overall size of Pu. pardoides is significantly smaller than that of A. pardinensis (the upper carnassial of Pu. pardoides is about 22 mm in average length5, while that of A. pardinensis is about 30 mm6). In the light of the above features, the felid from Monte Argentario is here referred to A. pardinensis. However, the occurrence of Panthera-like characters in the skull is noteworthy. Among them, the presence of stout and strong canines stands out. The linear dimensions (length and breadth) of these teeth fall in the uppermost part of the A. pardinensis range and, at least for the upper canine, are close to the lower values recorded for medium-sized pantherines like P. gombaszoegensis (Supplementary Tables S1–S2 and Supplementary Fig. S3). Similarly, the comparative analysis of the palatal sutures (clearly visible in ArgBsc1 for the first time in A. pardinensis) evidences further affinities with pantherine cats. In particular, the indented suture trend observed in the Monte Argentario skull recalls more the extant leopard and snow leopard than the cheetah and puma (Supplementary Fig. S4). Previous studies6,10,12 already highlighted that A. pardinensis retains Panthera-like, primitive morphological characters, but most of them relate to the neurocranium (e.g., the relatively elongated braincase, with high sagittal and nuchal crests and—as also visible in ArgBsc1—narrow frontals between the postorbital processes). The specimen from Monte Argentario shows some significant pantherine-like characters also in the splanchnocranium (i.e., teeth and palatal sutures). Nevertheless, at least as regards to canine dimensions, our results should be placed in the context of the overall A. pardinensis intraspecific variation. As in part predictable by the long-lasting stratigraphic distribution (from late Pliocene to Middle Pleistocene) and the wide geographical distribution (from Morocco to China), A. pardinensis exhibits a considerable variation in size, with body mass estimated (for adult individuals) from about 60 to 120 kg (Supplementary Table S3 and Supplementary Fig. S4). This variation led some scholars15,33,36 to consider A. pardinensis as a broad ‘macrospecies’ subdivided into several subspecies6: A. p. arvernensis from Les Étouaires (late Pliocene) and Tuozidong (early Early Pleistocene); A. p. aicha from North Africa (earliest Pleistocene); A. p. pardinensis from a number of European to central Asian sites (Early Pleistocene; Middle-Late Villafranchian LMA); A. p. linxiaensis (=‘Sivapanthera’ linxiaensis)10 from northern China (early Early Pleistocene); A. p. pleistocaenicus from Untermassfeld (late Early Pleistocene; Epivillafranchian stage)37 and China (=‘Sivapanthera’ pleistocaenica)11 (Early Pleistocene; Villafranchian LMA); A. p. intermedius from Hundsheim and Mosbach (Middle Pleistocene; Galerian LMA). However, the validity of this taxonomic model is questioned by the lack of clear morphological or biometrical differences between the different subspecies. The available estimated body masses for A. pardinensis suggest that the variation found is independent of the age and the geographical location of the finds (Supplementary Fig. S5). An emblematic case is represented by the earliest (i.e., Early Villafranchian LMA) European specimens attributed to this taxon, namely those of Villafranca d’Asti (Supplementary Fig. S6), Villarroya, and Les Étouaires, for which the predicted body masses are 70, 87, and 121 kg, respectively. Unfortunately, the existing data are not sufficient to understand if the intraspecific variation of A. pardinensis could be linked to ecogeographical dynamics and/or sexual dimorphism. However, actualistic comparisons with extant large-sized felids allow to hypothesise that the latter factor can be called into question for A. pardinensis. Sexual dimorphism in body mass occurs in all living felids, and is particularly marked in wide-range large-sized species. For example, the average weight difference between males and females is about 60% in the jaguar, 80% in the leopard, 85% in the lion and the tiger, and even 90% in the puma, while it is much smaller (~15%) in the cheetah38. We obtain interesting information if we try to free the interpretations on A. pardinensis from the stratigraphic influence, that is if we consider the few available sites for which it is possible to estimate body mass for more than one individual (which we can therefore hypothesise as being coeval). The difference between the lowest and highest predicted body mass is about 31% at Ahl al Oughlam, 33% at Saint Vallier, and 72% at Longdan. This suggests that sexual dimorphism may have played an important role in the intraspecific variation of A. pardinensis, as hypothesised by Petrucci et al.39 based on postcranial material from Pirro Nord. Although out of the scope of this work, the same can be said for the Eurasian jaguar P. gombaszoegensis, whose predicted body masses span from about 65 to 180 kg in all its chronological (about 1.9–0.3 Ma) and geographic (Europe and Western Asia) range, with peaks of variation of ~80% and even 90% for local samples such as those from the type locality of Gombaszög and Untermassfeld, respectively (Supplementary Table S4). Acinonyx pardinensis and P. gombaszoegensis co-occurred in Europe for about 1.4 Ma in the Early and Middle Pleistocene, and are reported together in at least seven sites (Olivola, Dmanisi, Upper Valdarno, Pirro Nord, Untermassfeld, Le Vallonnet, and Mosbach, in decreasing stratigraphical order), often in association with sabretooth cats like Megantereon and/or Homotherium6,39,40. This extraordinary concentration of large felids is unequalled in modern ecosystems and, moreover, must be included in the context of the rich diversity of the Late Villafranchian/Epivillafranchian large carnivore guilds, which included, among others, also hyaenids and canids41. Interspecific competition for prey must have been strong in such palaeoecosystems and subject to ecological mitigation strategies. These could have included temporal niche displacement (e.g., diurnal/nocturnal hunting) and/or different spatial distribution within the ecosystem6 (for example, in Venta Micena, geochemical data suggest that Megantereon and Panthera preferred forested areas whereas Homotherium and Lycaon hunted in more open habitats)42. The recognition of pantherine-like characters in the Monte Argentario felid—as well as in other A. pardinensis samples from other localities—must lead to reconsidering the ecological role of this species, whose choice of prey and hunting strategy was likely to be different from those of the living cheetah6,16. Furthermore, we hope that the approach followed in this work, i.e., the use of high-resolution µCT techniques, may also be followed in the future for similar cases, in order to extract as much information as possible from fossil remains of Plio-Pleistocene vertebrates. |
| Users browsing this thread: |
| 4 Guest(s) |